(1) Field of the Invention
The invention relates to a gear mechanism which is improved to remove backlash.
(2) Description of the Related Art
In the prior art, there is a device for removing or adjusting backlash of a gear mechanism in which a distance between the centers of two engaging gears are changed to adjust the backlash, after which members for supporting the shafts of the gears are secured by bolts. However, this device is not suitable for mass-production since, according to the device, the gear mechanism becomes complex. Moreover, in the gear mechanism with the device for removing or adjusting the backlash, readjustment of the distance between the centers of the gears must be carried out after the installation since the distance will increase due to the wear of the gears during long operation time.
In another prior art, a gear mechanism is well known which comprises a pair of gears engaging and a spring for biasing the gears to each other to reduce the distance between the centers of the gears. However, in order to prevent the spring from being push back during the operation, the spring must have a strength to bias the gears to each other by a biasing force corresponding to the maximum transmitted torque. Therefore, the gears will wear soon due to the biasing force which is larger than than a biasing force required to remove the backlash. Moreover, the torque transmitted by the gears are limited.
Further, there is a prior art device for removing backlash between two helical gears in which one of the two helical gears is split into two parts by a plane perpendicular to the rotational axis, between which a spring is provided for biasing the split two portions in the opposited direction along a shaft thereof. However, both the split gear portions must have sufficient strength to transmit the torque. Therefore, as a result, the other helical gear engaging both the split gear portions must have a strength two times of required for transmitting the torque, which results in increasing the weight and reducing the acceleration performance of a body driven by the gear mechanism.